The purpose of this study is to evaluate a new drug called SB-207266-A in the treatment of Irritable Bowel Syndrome (IBS). IBS causes a significant change in daily habits as well as a quality of life for the patient. Symptoms include evacuation after attemtping to pass stool, changes in stool frequency or consistency, passage of mucus or bloating. It is also estimated to be the cause of between 20-40% of all visits to gastroenterologists.